Upregulation of Class II HLA as a Marker of Antibody-Mediated Rejection in Heart Allografts

Abstract

In 2013, the ISHLT introduced the working classification for pathological changes associated with antibody-mediated rejection of the heart allograft, known as p-AMR. With two components H, for histologic changes, and I for immunolabeled markers associated with AMR, the proposed classification also suggests to use Class II HLA as a marker of endothelial integrity. We hypothesized that Class II HLA rather than a marker of mere endothelial presence, is a marker of endothelial activation, and therefore could be associated with the diagnosis of AMR. 838 heart allograft biopsies, collected from January 2016 to September 2018 at a single institution were evaluated for both morphologic (H/E) and immunolabeled changes of AMR. Biopsies were immunolabeled with immunofluorescence with antibodies against C4d, and for immunohistochemistry with antibodies against C3d, CD68 and Class II HLA. ISHLT criteria was used to classify the biopsies, and for Class II HLA, both the percentage and the stain intensity were recorded. 74.8% of biopsies showed either a H, I or a combined evidence of AMR. The percentage of endothelial HLA Class II staining was significantly correlated with the diagnosis of AMR (r=0.39). HLA Class II showed a spectrum of intensity, quantified as negative (0) to strongly positive (+3). The diagnosis of AMR significantly correlated with moderate (+2) and strong (+3) staining intensity for Class II HLA, as follow: H+I (OR 28.3, p 0.0001); H alone (OR 22.73, p 0.0001) and I alone (32.63, p 0.0001). Our study also confirmed the value of the other AMR markers proposed by the ISHLT, such as C4d, C3d and CD68 (all p 0.0001), but importantly, and in contrast to prior observations, we showed that the C4d focally positive category (10-50%) is also significantly correlated to the diagnosis of AMR (OR 12.25, p 0.0005). We confirmed our hypothesis that in heart allograft biopsies there is a spectrum of both percentage and intensity of HLA Class II in endothelial cells, and that its staining by IHC is a marker significantly correlated with the diagnosis of AMR. In addition, the group of focally positive C4d biopsies should be considered positive for the I component of the 2013 ISHLT classification, as this group of biopsies also correlated with the diagnosis of AMR.